1. Field of the Invention
The present invention relates to a television camera and particularly relates to a television camera in which flicker generated when a subject is photographed under illumination of a fluorescent lamp can be suppressed.
2. Description of the Prior Art
Conventionally, when a subject is picked up under illumination of a fluorescent lamp by using a television camera, there has been a problem in that the light intensity of the fluorescent lamp changes periodically in accordance with the frequency of the power source, so that a flicker is generated by a beat between the frequency of change of the light intensity and the field frequency of the television signal. An explanation about the causes and characteristics of flicker generation and a flicker suppressing method are described in Japanese Patent Unexamined Publication (JP-A) No. 56-149179. The Publication discloses a television camera in which a flicker component of a frequency (20 Hz in the case of the power source of 50 Hz) corresponding to the greatest common measure between the on-off frequency of the fluorescent lamp (ordinarily, twice as high as the power source frequency) and the field frequency is extracted from a video signal, and the extracted flicker component is fedback or fedforward to thereby cancel the flicker.
To prevent a flicker from occurring by the above-mentioned method, it is necessary to adjust the quantity of feedback or feedforward accurately.
Further, in an image pickup element, such as a MOS image pickup element or image pickup tube, of the type in which the charge accumulated in photodiodes arranged in the form of matrix or light receiving films is read out by successively scanning the photodiodes or light receiving films line by line, a flicker appears on a scene of television picture as if it moves with a frequency of 20 Hz, however, the flicker is put out in a video signal as a flicker of 100 Hz. That is, at any specific point on the scene of television picture, the flicker is appears at a frequency of 100 Hz. Accordingly, it is impossible to prevent this flicker by the method disclosed in the above Japanese Patent Unexamined Publication No. 56-149179.